The present invention relates to interpolymer latices and to a process for their preparation. It also relates to the applications of these latices, especially as binders and more particularly in the coating of paper.
The latices forming the subject of the invention are aqueous dispersions of particles, having a diameter essentially between 0.1 and 1 .mu.m (micron) and preferably between 0.1 and less than 0.5 .mu.m, of an interpolymer comprising (a) a copolymer A of butadiene, sytrene and at least one ethylenically unsaturated carboxylic acid, and (b) a polymer B of at least one halogenoalkyl or halogenoacetoxyalkyl ester of an ethylenically unsaturated monocarboxylic or dicarboxylic acid, polymer B being at least partially grafted onto the copolymer A.
For the purposes of simplification, the terms "halogenoalkyl ester" and "halogenoacetoxyalkyl ester" hereafter respectively denote either a halogenoalkyl or halogenoacetoxyalkyl ester of a monocarboxylic acid, or a halogenoalkyl or halogenoacetoxylalkyl monoester or diester of a dicarboxylic acid. Use of mixtures of halogenoalkyl ester and halogenoacetoxyalkyl ester is contemplated.
The interpolymer preferably comprises 85 to 99% by weight of copolymer A and 15 to 1% by weight of polymer B.
The copolymer A comprises, by weight, 15 to 85% by butadiene, 5 to 84% of styrene and 1 to 10% of at least one ethylenically unsaturated carboxylic acid, and preferably 25 to 55% by butadiene, 35 to 74% of styrene and 2 to 5%, of at least one ethylenically unsaturated carboxylic acid.
The polymer B comprises, by weight, 15 to 100% of halogenoalkyl or halogenoacetoxyalkyl ester and 0 to 85% of at least one ethylenically unsaturated compound which can be copolymerized with the halogenoalkyl or halogenoacetoxyalkyl ester.
According to the invention, the halogenoalkyl or halogenoacetoxyalkyl ester can be represented by the general formula: RCOOZ, in which formula Z represents:
the radical --C.sub.n H.sub.2n-m+1 X.sub.m, in which X represents a halogen atom, preferably chlorine and/or bromine, n is an integer ranging from 1 to 6 and preferably from 1 to 4, and m is a integer ranging from 1 to 5 and preferably from 1 to 3; or PA1 the radical --(CH.sub.2 --CHY).sub.n '--OOC--CH.sub.(3-m') X.sub.m', in which X has the same definition as above, n' is an integer from 1 to 4, m' is an integer from 1 to 3, and Y represents a hydrogen atom or a methyl group; and PA1 a linear or branched C.sub.2 -C.sub.4 alkenyl group; PA1 a linear or branched C.sub.2 -C.sub.4 chloroalkenyl group; or PA1 a radical --R'--COOZ', in which Z' represents a hydrogen atom or the radical Z, and R' represents a linear or branched C.sub.2 -C.sub.4 alkenylene group, a linear or branched C.sub.2 -C.sub.4 chloroalkenylene group or a group ##STR1##
R represents:
Representative halogenoalkyl or halogenoacetoxyalkyl esters are those derived from ethylenically unsaturated carboxylic acids possessing up to 6 carbon atoms, such as acrylic, methacrylic, itaconic, crotonic, fumaric, maleic, mesaconic and glutaconic acids, and also their chlorine derivatives such as chloroacrylic, chlorofumaric, chloromaleic and chloroitaconic acids.
According to an embodiment of the invention, that part of the interpolymer which is insoluble in isopropyl alcohol represents at least 75%, preferably 90 to 95%, of the interpolymer and includes, in the grafted state, 0.2 to 15% by weight (preferably 0.5 to 5% by weight) of the halogenoalkyl or halogenoacetoxyalkyl ester.
The proportion by weight of solids in the latices forming the subject of the invention is generally between 1 and 70% and preferably between 30 and 55%.
Amongst the ethylenically unsaturated carboxylic acids forming part of the composition of the copolymer A and, if appropriate, of the polymer B, there may be mentioned, in particular, acrylic, methacrylic, crotonic, maleic, fumaric, itaconic, mesaconic and glutaconic acids or mixtures of at least two of these acids.
As compounds which can be copolymerized to form polymer B with the halogenoalkyl or halogenoacetoxyalkyl ester, there may be mentioned, in particular, vinylaromatic compounds, vinyl halides, vinylidene halides, dienic compounds, carboxylic acid vinyl esters and acrylic compounds. There may be mentioned, more particularly, styrene, .alpha.-methylstyrene, para-tert.-butylstyrene, chlorostyrene, vinyltoluene, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, butadiene, isoprene, chloroprene, acrylic, methacrylic, maleic, fumaric and itaconic acids and chlorine derivatives of these acids, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, chloroacrylonitrile, vinyl acetate, acrylic acid esters such as methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, n-butyl acrylate and isobutyl acrylate, and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, n-butyl methacrylate and isobutyl methacrylate.
The process of the preparation of the latices according to the invention comprises the steps of preparing a latex of copolymer A by the emulsion polymerization of butadiene, styrene and at least one ethylenically unsaturated carboxylic acid, and then, in the presence of the latex of copolymer A, polymerizing the halogenoalkyl or halogenoacetoxyalkyl ester and, if appropriate, at least one ethylenically unsaturated compound which can be copolymerized with the halogenoalkyl or halogenoacetoxyalkyl ester.
The latex of copolymer A is prepared in a manner which is in itself known by the polymerization in aqueous emulsion of butadiene, styrene and at least one ethylenically unsaturated carboxylic acid, in the presence of at least one initiator and of at least one emulsifying agent, the concentration of the mixture of monomers in the reaction medium generally being between 20 and 60% by weight.
According to an embodiment of the invention, the halogenoalkyl or halogenoacetoxyalkyl ester, by itself or in the presence of at least one other ethylenic compound, is introduced during the polymerization of the comonomers of A and, preferably, after the comonomers of A have been copolymerized to copolymer A with a degree of conversion of at least 50%.
In the preparation of the copolymer A, the butadiene generally represents between 15 and 85% and preferably between 25 and 55% by weight of the total weight of the monomers to be polymerized. The styrene generally represents between 5 and 84% and preferably between 35 and 74% by weight of the total weight of the monomers to be polymerized. The amount of carboxylic acid used is generally between 1 and 10%, preferably from 2 to 5% by weight relative to the total weight of the monomers to be polymerized.
The monomers used can be introduced into the reaction medium in a mixture or separately and simultaneously, either all at once before the start of the polymerization, or in successive portions or continuously during the polymerization.
The emulsifying agents used are conventional anionic agents represented, in particular, by the fatty acid salts, alkylsulfates, alkylsulfonates, aryl-sulfates, arylsulfonates, alkylaryl-sulfates, alkylarylsulfonates, sulfosuccinates and alkyl-phosphates of alkali metals, and hydrogenated or unhydrogenated abietic acid salts. They are employed at a rate of 0.01 to 5% by weight relative to the total weight of the monomers.
The initiator, which is water-soluble, is represented more particularly by hydroperoxides such as hydrogen peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide and paramenthane hydroperoxide, and by persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate. The initiator is employed in amounts of between 0.05 and 2% by weight relative to the total weight of the monomers. If appropriate, the initiator is combined with a reducing agent such as sodium bisulfite or formaldehyde-sulfoxylate, a polyethyleneamine, a sugar such as dextrose or sucrose, or a metal salt. The amounts of reducing agent used vary from 0 to 3% by weight relative to the total weight of the monomers.
The reaction temperatures, which depends on the initiator used, is generally between 0.degree. and 110.degree. C. and preferably between 25.degree. C. and 90.degree. C.
The polymerization of the halogenoalkyl or halogenoacetoxyalkyl ester and, if appropriate, of a compound which can be copolymerized with the halogenoalkyl or halogenoacetoxyalkyl ester, in the presence of the copolymer A, is carried out in aqueous emulsion, in the presence or absence of an emulsifying agent, a polymerization initiator and, if appropriate, a transfer agent, the total concentration of copolymer A+monomer(s) (halogenoalkyl or halogenoacetoxyalkyl ester(s) and copolymerible compound(s)) in the reaction medium being between 20 and 70% by weight.
The amount of latex of copolymer A used is such that the copolymer A generally represents 80 to 99% by weight of the total weight of copolymer A+monomer(s).
The initiator, which is identical to or different from that used for the preparation of the copolymer A, is chosen from amongst the initiators mentioned above. It is employed in amounts of between 0.05 and 6% by weight relative to the monomer(s).
The emulsifying agent present in the latex of copolymer A is generally sufficient to maintain the stability of the emulsion during the polymerization of polymer B. However, in certain cases, it may be necessary to add an additional amount of an emulsifying agent identical to or different from that used for the preparation of the copolymer A. Representative emulsifying agents are listed above. The emulsifying agent is introduced at a rate of 0 to 2.5% by weight relative to the total weight of copolymer A+monomer(s).
The transfer agent, used in proportions ranging from 0 to 3% by weight relative to the monomer(s), is generally chosen from amongst mercaptans such as N-dodecylmercaptan and tert.--dodecylmercaptan, cyclohexane, and halogenohydrocarbons such as chloroform, bromoform and carbon tetrachloride. The transfer agent controls the proportion of grafted polymer and the length of the grafted molecular chains. It is added to the reaction medium either before the polymerization or during polymerization.
The reaction temperature, which depends on the monomer to be copolymerized with the halogenoalkyl or halogenoacetoxyalkyl ester and on the initiator used, is generally between 0.degree. and 110.degree. C. and preferably between 25.degree. and 90.degree. C.
The latices according to the invention are particularly useful as binders for the preparation of aqueous compositions for coating paper, and more particularly for offset printing paper.
It is known that, in principle, aqueous compositions for coating paper contain pigments and binders. The pigment most commonly used in mineral clay. It is also possible to use a small proportion, relative to the mineral clay, of other pigments such as calcium carbonate, titanium oxide, satin white, hydrargillite, talc or barium sulfate. These pigments are dispersed in water, generally in an alkaline medium and in the presence of dispersing agents, the most important of which are tetrasodium pyrophosphate, sodium hexametaphosphate and low molecular weight polyacrylates, in amounts of between 0.2 and 0.5% by weight relative to the pigments.
These pigments are fixed to the paper by means of binders. Binders which have already been proposed for this application are aqueous latices of a synthetic polymer such as a butadiene/styrene copolymer, a carboxylated butadiene/styrene copolymer, an acrylic polymer or a vinyl acetate polymer, employed either by themselves or in a mixture with natural binders such as starches, proteins or casein, or synthetic binders such as polyvinyl alcohols. A particularly advantageous category of synthetic binders consists of the latices of carboxylated butadiene/styrene copolymers comprising, by weight, 30 to 50% of butadiene, 40 to 68% of styrene and 2 to 10% of at least one ethylenically unsaturated carboxylic acid. Products capable of improving the water retention properties of the coating compositions, such as carboxymethylcelluloses or alginates, can also be combined with the latices.
Finally, the coating compositions can contain a variety of other ingredients such as crosslinking agents, anti-foam agents, slip agents and fluorescent brighteners.
The coating of paper with the aid of the aqueous compositions is carried out by a variety of techniques using a variety of coating machine devices, such as the air knife coating machine, the size press, the Champion coating machine, the Massey coating machine and the trailing doctor. After coating, the paper undergoes a drying operation, which is generally followed by a calendering operation.
Wet picking resistance is a particularly important property for coated offset printing paper. Specifically, the offset printing process, which is based on the repulsion of water by greasy inks, uses water. In four-color offset printing, it is consequently necessary to print the second, third or fourth color in a place which has already been wetted. Thus, to avoid picking in the wet state, which clogs the blanket and the offset presses, it is important for the paper to possess an adequate wet picking resistance.
The wet picking resistance of a coated paper produced by the latices according to the invention is higher than that of a coated paper produced by the latices of the corresponding copolymers A.
Examples 1 to 11 which follow, in which the parts are indicated by weight, illustrate, but do not limit, the invention.